Apparatus for continuous heat processing of ore pellets

ABSTRACT

Apparatus and method for preheating, hardening and reducing ore pellets that provide for envelopment of the pellets in inert particulate material throughout the processing. Green pellets are continuously charged into a fluidized bed of heated particulate material and preheated while being buoyantly moved to a second fluidized bed. The preheated pellets are then buoyantly transported through the second fluidized bed of particulate material, which is at a higher temperature than the first bed, while being hardened. Hardened pellets are directly discharged from the second bed to the upper region of a columnar reactor for random envelopment within a bed of inert particulate material that is heated to a temperature sufficient to reduce the pellets during downward movement through the reactor.

7 1 United States atent 1191 1111 3,776,533 Vlnaty 1451 Dec. 4, 1973[54] APPARATUS FOR CONTINUOUS HEAT 3,539,336 11/1970 Urich 1 75/3PROCESSING OF ORE PELLETS 3,172,757 3/1965 Hess 75/68 3,005,701 10/1961Eberhardt.... 75/34 Inventor: J p y, q pp 3,043,652 7/1962 Schytil 18/20[73] Assignee: Dravo Corporation, Pittsburgh, Pa.

Primary ExaminerL. Dewayne Rutled e [22] Flled: 1970 AssistantExaminerPeter D. Rosenberg [21] Appl. No.: 6,433 AttorneyParmelee,Utzler and Welsh [52] US. Cl 266/24, 75/3, 75/9, [57] ABSTRACT 51 1m.(:1 C2lb 11 5/12 Appafatus and method hardening and 58 Field of Search75/3, 4, 9, 26, 34, educmg F Pellets Pmvde 9 envehpment of 75/6 1;266/24; 18/20 the pellets in inert particulate material throughout theprocessing. Green pellets are continuously charged [56] References Citedinto a fluidized bed of heated particulate material and preheated whilebeing buoyantly moved to a second UNITED STATES PATENTS fluidized bed.The preheated pellets are then buoy- Renzoni transported through theecond fluidized of 2,874,480 2/1959 Todd 75/26 particulate material,which is at a higher temperature 331L466 3/1967 i 75/26 than the firstbed, while being hardened. Hardened 2,848,316 8/1958 Davis 75/262,129,760 9/1938 Greenawalt." 75/8 pellets are directly d1scharged fromthe second bed to 2,864,686 12/1958 Agarwal the upper region of acolumnar reactor for random en- 3,49o,895 1/1970 svenssonm 75/3velopment within a bed of inert particulate material 2 394 331 19 1 01 224 that is heated to a temperature sufficient to reduce the 3,028,2314/1962 Klemantaski 266/24 pellets during downward movement through thereac- 3,356,488 12/1967 Walsh 75/26 tor. 3,495,971 2/1970 Ban 75/33,160,496 12/1964 Vaccari 75/6 9 Claims, 1 Drawing Figure [run are 000/p/Icl! reforming apparlus wafer reduced lmn ide 1 APPARATUS FORCONTINUOUS HEAT PROCESSING OF ORE PELLETS BACKGROUND OF THE INVENTION Itis known to produce compacts such as pellets or briquettes from iron oreand a solid reducing agent and to directly reduce the compacts while ina solid state. Problems of operation and inefficiency have, however,prevented the acceptance of such solid state reducing methods on a largecommercial scale. The problem of breakage of the pellets duringpreheating and hardening steps has usually required that the pellets beprepared in an apparatus separate from a direct reduction apparatus,under carefully controlled conditions. The pellets are then reheatedwhile transferring them to a direct reducer. Transferring pellets in anycase subjects them to abrasive action and damage. The fragile nature ofthe pellets during direct reduction also causes problems in a reducingapparatus where pellets are conventionally rotated, rolled, or otherwisemoved through a highly heated zone in large quantities, in which casethe weight of the upper pellets in the mass results in breakage ofpellets below. Even with breakage kept to a minimum, during exposure tothe high temperatures needed for direct reduction, the surface of thepellets may flux and the pellets fuse together to form clumps or buncheswhich are difficult to separate and process.

Since the heat requirements for direct reduction of ores are high, anyheat supplied must be effectively utilized in order to achieveeconomical processing. Indirect heating, such as by heating the exteriorof a direct reduction apparatus, is expensive while the use of burnerswithin a reducer for direct heating often results in diversetemperatures within various regions of the reducer andresulting hotspots.

The need thus exists for a process and apparatus for preheating,hardening and reducing pellets, such as iron ore pellets, where breakageor attrition of pellets is maintained at a relatively insignificantproportion throughout and where the pellets are economically andefficiently reduced. This invention is an improvement over the inventiondescribed in US. Pat. No. 3,585,023 issued June 15, 1971 by George A.Snyder and the present inventor, where the reduction of iron ore pelletsis carried out by introducing pellets into a heat exchange medium ofhighly-heated, non-reactive solid particles.

SUMMARY OF THE INVENTION In accordance with the present invention,pellets are continuously heat-processed through the stages of drying andpreheating, hardening, and reduction with the pellets enveloped in inertparticulate material throughout all stages of processing. Pellets areformed in a conventional apparatus and discharged into a first enclosurecontaining a fluidized bed where they are dried and preheated whilebeing buoyantly moved through the enclosure. The dried, preheatedpellets are then directly discharged into a second enclosure having afluidized bed that is at a higher temperature than the first. Thepellets are subjected to incipient hardening while buoyantly movedthrough the second enclosure and are then discharged into a columnarreactor where they are enveloped in a highly heated bed of inertparticles for reduction. The mixture of pellets and inert materialdescends by gravity through the reactor where they are reduced andfinally separated. When the pellets contain zinc oxide or othercompounds of volatile metals, these metals can also be reduced in thecolumnar reactor and collected. The pellets are thus protected from anysignificant breakage or attrition throughout the heat processing and arecontinuously and efficiently processed.

BRIEF DESCRIPTION OF THE DRAWING The drawing schematically illustratesan apparatus embodying the invention, and is also a flow diagramillustrating the present process.

DETAILED DESCRIPTION As illustrated in the drawing, the apparatusincludes a pelletizing apparatus and a fluidized bed type preheating andhardening furnace for pellets. The preheating fluidized bed furnace 2comprises a horizontally disposed enclosure with fluidizing gas inletlines 3 at the lower portion thereof and an inlet means 4 for charginghot finely divided inert solids into the enclosure. The chargedfluidizing gas and finely divided inert solids make up the fluidized bedused in the preheater. Herein, the term fluidized bed is used in itsconventional sense, that is, one in which a mass of finely dividedsolids is kept in a suspended state by a gas, the mass having aliquid-like mobility. The fluidizing gas inlets 3 are so arranged thatin addition to suspending the finely divided solids, they providetranslational movement of pellets within the fluidized bed preheater,whereby green pellets introduced through an inlet means 5 at one end ofthe enclosure are moved toward a discharge means 6 at the other end ofthe enclosure, the pellets being preheated during such transition. Ascreen or grid 7 extends across the lower portion of the enclosure 2through which the fluidizing gas passes but which supports the finelydivided solids and pellets. The finely divided inert solids used in thepreheater are those which will form a fluidized bed and not react withthe pellets, such as sand, alumina, silicon carbide, chrome-magnesite orother fine refractory material.

A mixture of iron oxide concentrate and carbonaceous fuel, which servesas a reducing agent, is mixed in pelletizer 8, such as a disc or drumpelletizer and the mixture formed in a conventional manner into greenpellets. Generally, about 8-14 percent water is added to the mixturealong with a binder, if required, and the mixture rolled into pellets orcompacts. The iron oxide may be natural ore or ore concentrates infinely divided form; flue dust from basic oxygen furnaces; iron oxidesfrom other sources or mixtures thereof. The reduction of pyriteroastings which contain various impurities such as zinc, copper, tin,arsenic, lead or sulfur can also be carried out according to the presentinvention, where about 3-5 percent calcium chloride or other halide isadded to the pellets to react with these impurities. In such pyritereduction, volatile metal compounds are formed and removed during thepreheating and hardening stages. The carbonaceous fuel admixed with theiron oxides is coal, coke, anthracite, bituminous coal or other fossilfuel. A binder such as a coal tar pitch may also be added to the mixtureto provide a strongly adhered pellet. The pelletizing apparatus andprocedure used are well known and various modifications and changes inpelletizing specific iron oxides would, of

' course, be obvious to one skilled in the art.

From the pelletizer 8, pellets are moved throug charging means 5, whichcontains a valve 5a, and introduced into the fluidized bed preheater 2.Since both the finely divided solids and the fluidizing gas are heatedto a predetermined temperature sufficient to preheat the pellets, thefluidized bed acts as a heat transfer medium for preheating the pellets.In addition to providing rapid and complete preheating of the compacts,the fluidized bed provides a cushioning for the green pellets which arefragile and easily subject to breakage or attrition. The temperature ofthe fluidized bed preheater will vary depending upon the specificcomposition of the compacts and the presence or absence of water in thepellets, but for iron oxide pellets will generally be in the range of400-l200 F. The pitch or volatile tar ingredients and other volatilematter in the pellets, such as low temperature volatile metalimpurities, are exhausted from the preheater 2 through an exhaust line 9and the tar or other volatile matter separated in a cooler 10 beforebeing discharged from the apparatus through line 11.

Adjacent the discharge end of the preheating furnace there is provided afluidized bed furnace 12 for incipient hardening of the pellets.Fluidizing gas is fed to the horizontally disposed enclosure 12 throughlines 13 and finely divided inert solids are introduced through inletline 14 to provide the fluidized bed. A screen 15 is provided across thelower portion of the enclosure. An inlet means 16 to the furnace 12 isadjacent the discharge means 6 of the preheater and pellets from thepreheater are transported to furnace 12 and then through the furnace toa discharge means 17 by the buoyant translational motion of thefluidized bed, similar to the movement of pellets through the preheater2. The temperature within the fluidized bed 12 used for incipienthardening of the pellets, is for iron oxide pellets,maintained at about1400-l800F this temperature being sufficient to heat harden the pelletsand carbonize the fuel contained therein, but below that at whichsignificant reduction of iron oxide will take place. A non-oxidizing oronly a slightly oxidizing atmosphere is maintained in the enclosure 12so as to preserve the carbonaceous material in the pellets during theincipient hardening.

Pellets from the preheater 2, along with some carryover finely dividedsolids from the preheater fluidized bed, are exhausted from thepreheater through discharge means 6, which contains a screen or grid 18for separation of the preheated pellets and the finely divided solids.The grid 18 is constructed such that the finely divided solids will passthrough while the preheated pellets are supported and transferredtherealong to the inlet means 16 of hardener 12. The finely dividedsolids passing through grid 18 are collected in an enclosed chamber 19and returned by line 20 pneumatically, or by gravity flow or othermeans, to a fluidized bed reheating device 21 where the finely solidsare reheated to a temperature of about 400-1200F. and used to replenishthe supply of solids in the preheater 2. The preheated pellets are thencharged into enclosure 12 through inlet means 16, where the pellets aresuspended in the fluidized bed thereof and heated to l400-l800F. whilebeing transported threthrough. Off-gases from the enclosure 12 areexhausted through line 22 and can be used in a heat recuperator 23 forair preheating, steam generation, or the like, prior to being dischargedthrough line 24 to the atmosphere. In the case of treatment of pyriteroastings, metal halides formed from halides which were added to thepyrites during pelletizing and the metals contained therein, would alsobe contained in the off-gases and would be removed in recuperator 23.

The discharge means 17 for removal of hardened pellets from theenclosure 12 contains a grid or screen 25 through which finely dividedsolids pass and which will separate the finely divided solids from thepellets. The finely divided solids are collected in a chamber 26 andreturned by conduit 27 to the fluidized bed solids reheater 21.

The fluidized bed reheater 21 for heating of the finely divided solidsused in the fluidized beds of the preheating and hardening furnaces isof conventional design and it is only schematically illustrated. Asshown, two sections 28 and 29 are preferably provided, with the lowersection 28 being used to preheat the solids to a higher temperature thanthe temperature of solids in section 29. An inlet 30 for gases isprovided at the bottom of the cylindrically shaped reheater and there isa gas outlet 31 at the top. A grid or screen 32 is provided in the lowersection 28 through which gases are passed, the grid holding a supply offinely divided solids 33. A second grid 34 is situated intermediate thetwo sections 28 and 29 of the reheater and holds a supply of finelydivided solids 35 in the upper section 29. Two separate supplies offinely divided solids 33 and 35 are thus available for use in the twofluidized bed furnaces 2 and 12. Charging means 28a and 29a are providedto enable addition of make-up solids. Highly heated gases are charged tothe reheater 21 from inlet line 30 through grid 32 which first heat thesupply 33 to the desired temperature, preferably in the range ofl400l800F. 'The gases which will be somewhat cooler after contact withsupply 33 then are passed through grid 34 to heat the supply 35 to thedesired temperature, preferably on the order of 400l200F. A portion ofthe hot gases from lower section 28 of the reheater are discharged fromthe reheater 21, these gases being on the order of l400-1800F., throughline 36, which may contain a valve 37, or other regulating device, andare fed through inlets 13 of the enclosure 12, for use as fluidizinggas. At the same time, hot finely divided solids are carried throughconduit 38 at a predetermined rate to replenish the supply of solids inthe fluidized bed of enclosure 12. The gases through line 36 and thesolids through conduit 38 are thus at the temperature required forincipient hardening of the pellets in the enclosure 12. While thefluidized bed is replenished in this manner, separated finely dividedsolids from enclosure 12 are returned to section 28 of preheater 21through line 27 and inlet 39 to maintain the supply 33 of solids. Aportion of the hot gases from the upper section 29 of the reheater 21are discharged from line 31 through line 40 which contains a regulatingvalve 41 and are fed to the inlet lines 3 of the preheater 2. Also,solids from the upper section 29 of reheater 21 are charged to the inletmeans 4 of the preheater 2 through conduit 42, the solids from conduit42 and gases from line 40 providing the fluidized bed in the preheater2. Finely divided separated solids from the preheater section passthrough line 20 and are charged through inlet 43 to replenish the supply35 in the upper section 29 of reheater 21. Residual off-gases from thereheater 21 are exhausted through line 44.

After the pellets have been transported through enclosures 2 and 12,wherein they have been preheated and incipiently hardened, the pelletsare charged to a reduction reactor comprising a refractory linedvertical column 45. The reduction reactor is similar to the reactordescribed in US. Pat. No. 3,585,023. The column 45 has a mixing chamber46 at the top into which pellets from discharge means 17 of the hardener12 are introduced and an inclined grate 48 at the bottom portion. Afeeder 47 such as a vibrator is provided in the column to assist in theflow of a solid mixture downwardly through the column 45.

The pellets are mixed in chamber 46 with hot inert particulate solids,which solids will not react with the iron oxides or other oxides presentin the compacts. The inert solids which may be silicon carbide, sand, orother refractory material are heated to a temperature in the range ofl800-2500F. prior to being mixed with the compacts. Such mixture rapidlyheats the compacts to reduction temperature while cushioning thecompacts and maintaining individual compacts separate from others duringgravity flow through the vertical reactor, the hot inert solids arecharged to the reactor in an amount of about 4:1 to 8:1 weight ratiorelative to the compacts, with preferably a ratio of about 5 to 1 beingused.

The mixture descends by gravity in the reactor to the grate 48 that isconstructed so as to allow the passage of hot inert solids such as sandtherethrough but will support the pellets and lead the reduced pelletsto a closed discharge chute 49 having a star valve or other lock device50. A discharge chute 51 below the grate -48 carries the sand to an airlift furnace 52. Specifically, an air lift furnace 52, of knownconstruction, comprises a refractory lined column 53 having a combustionzone 54 at its lower portion and means for charging air and fuel to thecombustion zone illustrated as line 55 for air and line 56 for fuel,these being mixed and burned in a burner 57. The combustion gases arefed to the combustion zone and carry the sand up the column 53 to ahopper 58 at the top of the column. A discharge chute 59 is providedfrom hopper 58 leading to the top portion 46 of the reactor column, witha regulating device 60 provided to regulate the flow of hot sand to themixing chamber 46 of column 45. The hot combustion gases from the airlift furnace, after deposition of the hot solids into hopper 58 aredischarged through conduit 6] which carries the highly heated gases toline 30 for use in the fluidized bed reheater.

The reduced pellets are discharged through chute 49 by regulator 50 andintroduced into a cooling tank 62 where they are cooled by contact witha non-oxidizing gas introduced through line 63. The non-oxidizing gaspasses countercurrently to the descending reduced pellets in the coolerand is exhausted through line 64 to tuyeres 65 and into the reducer 45where the gases flow countercurrently to the descending mixture and aidin the reduction of the pellets in the reactor 45. From the cooler 62,the reduced pellets are discharged through a discharge valve 66 andconduit 67 into a further cooling device such as a water cooled rotatingdrum 68 and then are discharged from the apparatus through chute 69.

The reduction is continuous, with preheated, incipiently hardenedpellets and hot inert solids being mixed at the top of the reactor. Themixture descends by gravity with the rate of descent depending upon theamount of pellets in the mixture, the rate of removal and the contacttime required for reduction. During the reduction, the reaction of themetal oxides in the pellets with the carbonaceous material present, asis well known, will produce carbon monoxide and water. When zinc oxidesor other compounds of volatile metals are present in the hardenedpellets, such as when pellets formed from BOF dust are being processed,the zinc oxide is also reduced and the zinc vapors carried off with thecarbon monoxide gases. The off gases from reactor 45 are exhaustedthrough a conduit 70 to a cooler 71 wherein volatile metals such as zincare liquified. The condensed metal is collected in the cooler 71 and isperiodically tapped through line 72. The carbon monoxide bearing gasesflow from cooler 71 through line 73 to a condenser 74 where watercarried by the off gases is condensed and removed. The carbon monoxidegases then pass through line 75 to a compressor 76. The residual,relatively clean carbon monoxide discharged from the compressor 76 flowsthrough line 77 to a reformer 78, where, in conventional manner, carbonmonoxide is catalytically reformed in the presence of steam suppliedthrough line 79. Such reforming devices, where carbon monoxide and steamare reacted to produce hydrogen gas, are well known in the art. Thereaction products from the reformer 78 flow to a pressure cooler 80where associated carbon dioxide and water vapor are removed while thehydrogen gas is conducted through line 81 to the cooling tank 62 andsubsequently into the reactor for use as a reductant.

From the foregoing it will be seen that the freshlyformed green pelletsare dropped in continuous succession into an ebullient bed offinely-divided preheated solids into which hot gases are continuouslycirculated, so that the pellets avoid any severe shock as they fall intothe bed and are buoyed or floated at random along the bed substantiallyout of contact with one another, so that they are preheated and driedwithout the breakage, deformation or attrition that occurs in otherprocesses, such as in shaft furnaces, kilns, etc. After the initialpreheating in this environment to a temperature of the order of 400-1200F. they are discharged from the opposite end of the preheater alongwith the particulate stream of fluidized particles in which they aremoved. The particles are screened out, returned to the upper section 29of the heater 21 to be reheated and recycled to the preheater, while thepellets, passing over the screen, enter the second fluidized bed unitwhere they are similarly enveloped in more highly-heated gases andbuoyed by the second fluidized bed toward the discharge end, beinghardened under the same protection against damage that they had in thepreheater. Leaving the second fluidized bed at a temperature between1400F. and 1800F., they are now hard enough and sufficiently bonded toendure the reducing operation in the columnar reactor. As in thepreceding fluidized bed unit, the discharge from the second unit isscreened with the pellets discharging in continuous procession into thetop of the columnar reactor and the screenings are transferred to thelower portion 28 of the heater 21 to be heated and recycled to thesecond fluidized bed.

At the top of the reactor the hot pellets are enveloped in the stillmore highly-heated fine particles which are also dischargingcontinuously into the top of the reactor, so that the pellets are forthe most part arranged at random and separated one from another whilethey are heated to reduction temperature. Reduction of the pellets takesplace while they are randomly separated, through heating thecarbonaceous material-containing pellets to reducing temperature. Theydescend with the hot particulate material preferably countercurrent tohydrogen or other reducing gas introduced into the column through abustle pipe and tuyeres 65. This reducing gas, having been used to coolthe pellets in cooling unit 62, assists in the usual reducing reaction,with the pellets being converted principally to metal, but withoutdeformation or bunching. The gaseous reaction products are removed nearthe top of the column. Since the pellets are embedded in and envelopedby the surrounding hot particles, they are more uniformly heated acrossthe section of the column than is the case with shaft furnaces or withtraveling grates. While there is of course an increasing pressure in themass downwardly in the column, the pressure is not concentrated in thepellets as is the case in a shaft furnace, for example, where a pellettheoretically makes only point contact with a pellet or pellets belowit, placing them under severe crushing pressures.

I claim:

1. Apparatus for the continuous heat processing of pellets,characterized by the cushioning of the pellets during preheating andincipient hardening to minimize breakage or attrition, wherein thepellets are enveloped in inert particulate material at all stages ofprocessing comprising:

a. a pellet-forming apparatus,

b. a first enclosure containing a fluidized bed of solid particles ofinert material arranged to continuously receive green pellets andbuoyantly move them to a point of discharge with means for maintainingthe fluidized bed at an elevated temperature to preheat and dry thepellets as they are carried to the point of discharge,

c. a second enclosure containing a fluidized bed similar to the firstinto which the dry preheated pellets from the first unit are directlydischarged, said second enclosure having means for maintaining thefluidized bed at a temperature higher than the first to effect incipienthardening of the pellets,

d. means for charging fluidized gas to each of said enclosures soarranged as to direct the movement of the pellets through saidenclosures,

e. a columnar reactor arranged to continuously receive hardened pelletsdirectly from said second enclosure at its upper end, said reactorhaving means for continuously supplying highly-heated inert particulatematerial into the upper end thereof to envelop the pellets as they aredischarged into the upper end thereof, and

f. means at the bottom of the reactor for continuously removing andseparating pellets and particulate material to effect a continuousdownward movement of the pellets and particulate material through thecolumn at a controlled rate,

g. said apparatus thereby effecting the processing of the pelletscontinuously while they are randomly enveloped in and separated by hotinert particulate material.

2. Apparatus for the continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 1 including means for separating driedand preheated pellets from said solid particles of inert materialdischarged from said first enclosure prior to charging of said pelletsinto said second enclosure.

3. Apparatus for the continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 2 including means for reheating andreturning said separated inert material for recycle to said firstenclosure.

4. Apparatus for continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 2 including means for separating hardenedpellets from solid particles of said fluidized bed discharged from thesecond enclosure prior to envelopment of said pellets in said columnarreactor.

5. Apparatus for continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 5 including means for reheating andreturning said separated solid particles of said fluidized bed of thesecond enclosure for recycle to said second enclosure.

6. Apparatus for continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 1 including means for charging a reducinggas to the lower portion of said columnar reactor for countercurrentflow to said movement of pellets and particulate material.

7. Apparatus for continuous heat processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 1 including means for exhausting gasesfrom said columnar reactor and means for cooling said exhaust gases toremove volatile metals present therein.

8. Apparatus for use in the manufacture of pellets containingagglomerated mineral particles comprising:

a. a pelletizing unit for continuously forming moist green pellets,

b. an enclosure into which the moist green pellets are discharged bygravity, said enclosure containing a fluidized bed of heatedfinely-divided inert particulate material to cushion the pellets as theygravitate into the enclosure and through which they become randomlydistributed,

0. means for continuously progressing said bed from one end of theenclosure toward the other while maintaining the bed in a heatedcondition and discharging the material and pellets from the other end,whereby the pellets are dried and preheated while buoyed in said bed,

d. means for separating the preheated and dried pellets from theparticulate material upon discharge at said other end, and

e. means for heating and recycling the separated particulate material tothe end of said enclosure into which the moist green pellets aredischarged.

9. Apparatus for use in the manufacture of pellets 4 containingagglomerated mineral particles as defined in claim 8 including:

a. a second enclosure containing a fluidized bed of heatedfinely-divided inert particles,

b. means for transferring dried and preheated pellets from the firstenclosure directly to said second enclosure,

c. the fluidized bed of said second enclosure being at a temperatureseveral hundred degrees higher than the fluidized bed in said firstenclosure wherein the preheated and dried pellets are continuouslyenveloped and buoyed in the fluidized bed of the second enclosure inrandom'distribution from the end into which the pellets are transferredfrom the first enclosure to the other end from which the pellets aredischarged to harden the pellets for further processmg.

1. Apparatus for The continuous heat processing of pellets,characterized by the cushioning of the pellets during preheating andincipient hardening to minimize breakage or attrition, wherein thepellets are enveloped in inert particulate material at all stages ofprocessing comprising: a. a pellet-forming apparatus, b. a firstenclosure containing a fluidized bed of solid particles of inertmaterial arranged to continuously receive green pellets and buoyantlymove them to a point of discharge with means for maintaining thefluidized bed at an elevated temperature to preheat and dry the pelletsas they are carried to the point of discharge, c. a second enclosurecontaining a fluidized bed similar to the first into which the drypreheated pellets from the first unit are directly discharged, saidsecond enclosure having means for maintaining the fluidized bed at atemperature higher than the first to effect incipient hardening of thepellets, d. means for charging fluidized gas to each of said enclosuresso arranged as to direct the movement of the pellets through saidenclosures, e. a columnar reactor arranged to continuously receivehardened pellets directly from said second enclosure at its upper end,said reactor having means for continuously supplying highlyheated inertparticulate material into the upper end thereof to envelop the pelletsas they are discharged into the upper end thereof, and f. means at thebottom of the reactor for continuously removing and separating pelletsand particulate material to effect a continuous downward movement of thepellets and particulate material through the column at a controlledrate, g. said apparatus thereby effecting the processing of the pelletscontinuously while they are randomly enveloped in and separated by hotinert particulate material.
 2. Apparatus for the continuousheat-processing of pellets wherein the pellets are enveloped in inertparticulate material at all stages of processing as defined in claim 1including means for separating dried and preheated pellets from saidsolid particles of inert material discharged from said first enclosureprior to charging of said pellets into said second enclosure. 3.Apparatus for the continuous heat-processing of pellets wherein thepellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 2 including means for reheating andreturning said separated inert material for recycle to said firstenclosure.
 4. Apparatus for continuous heat-processing of pelletswherein the pellets are enveloped in inert particulate material at allstages of processing as defined in claim 2 including means forseparating hardened pellets from solid particles of said fluidized beddischarged from the second enclosure prior to envelopment of saidpellets in said columnar reactor.
 5. Apparatus for continuousheat-processing of pellets wherein the pellets are enveloped in inertparticulate material at all stages of processing as defined in claim 5including means for reheating and returning said separated solidparticles of said fluidized bed of the second enclosure for recycle tosaid second enclosure.
 6. Apparatus for continuous heat-processing ofpellets wherein the pellets are enveloped in inert particulate materialat all stages of processing as defined in claim 1 including means forcharging a reducing gas to the lower portion of said columnar reactorfor countercurrent flow to said movement of pellets and particulatematerial.
 7. Apparatus for continuous heat processing of pellets whereinthe pellets are enveloped in inert particulate material at all stages ofprocessing as defined in claim 1 including means for exhausting gasesfrom said columnar reactor and means for cooling said exhaust gases toremove volatile metals present therein.
 8. Apparatus for use in themanufacture of pellets containing agglomerated mineral particlescomprising: a. a pelletizing unit for continuously forming moist greenpellets, b. an Enclosure into which the moist green pellets aredischarged by gravity, said enclosure containing a fluidized bed ofheated finely-divided inert particulate material to cushion the pelletsas they gravitate into the enclosure and through which they becomerandomly distributed, c. means for continuously progressing said bedfrom one end of the enclosure toward the other while maintaining the bedin a heated condition and discharging the material and pellets from theother end, whereby the pellets are dried and preheated while buoyed insaid bed, d. means for separating the preheated and dried pellets fromthe particulate material upon discharge at said other end, and e. meansfor heating and recycling the separated particulate material to the endof said enclosure into which the moist green pellets are discharged. 9.Apparatus for use in the manufacture of pellets containing agglomeratedmineral particles as defined in claim 8 including: a. a second enclosurecontaining a fluidized bed of heated finely-divided inert particles, b.means for transferring dried and preheated pellets from the firstenclosure directly to said second enclosure, c. the fluidized bed ofsaid second enclosure being at a temperature several hundred degreeshigher than the fluidized bed in said first enclosure wherein thepreheated and dried pellets are continuously enveloped and buoyed in thefluidized bed of the second enclosure in random distribution from theend into which the pellets are transferred from the first enclosure tothe other end from which the pellets are discharged to harden thepellets for further processing.